The present invention relates to a sputtering target made from a Ni—P alloy or a Ni—Pt—P alloy for use in forming thin films via the sputtering method, and to a method of producing such a sputtering target.
Thin films made from a Ni—P alloy or a Ni—Pt—P alloy are used in hard disks and other magnetic recording mediums. These thin films are generally formed by sputtering a target made from a Ni—P alloy or a Ni—Pt—P alloy. As is well known, sputtering is a method of depositing a thin film, which has the substance configuring the target material as its basic component, on a substrate facing the target by sputtering grains from the target by the bombarding energy due to Ar ion irradiation toward the target. Since the target material collides with, and is accumulated on, the substrate surface in a high energy state, it is possible to form a dense film.
In relation to a Ni—P alloy target, for instance, Patent Document 1 discloses a Ni—P alloy sputtering target containing 12 to 24 at % of P, oxygen in an amount of 100 wtppm or less, and remainder being Ni and unavoidable impurities, wherein this sputtering target is produced by melting a Ni—P alloy base metal having an oxygen content of 10 wtppm or less and atomizing the product in an inert gas atmosphere to obtain an atomized powder having an average grain size of 100 μm or less, and thereafter hot pressing or hot isostatic pressing the obtained atomized powder. Patent Document 1 additionally describes that, according to this invention, it is possible to inhibit abnormal discharge, and prevent the generation of particles.
Patent Document 2 discloses a method of producing a Ni—P-based target including the steps of obtaining a gas atomized powder having Ni and P as its main components, thereafter causing the maximum grain size of the obtained gas atomized powder to be 100 μm or less via classification and/or pulverization, and subsequently performing pressure sintering. Patent Document 2 additionally discloses a Ni—P-based target having a maximum grain size of 100 μm or less, and an oxygen content of 300 ppm or less. Patent Document 2 describes that, according to this invention, the surface roughness of the eroded portion of the target will be finer than 10 μm Rmax, and the generation of foreign substances can be inhibited.
Patent Document 3 discloses a method of producing a sputtering target, wherein the compact obtained by thermally solidifying and molding a powder is cooled from a temperature near the molding temperature to 300° C. at a cooling rate of 144° C./hr to 36000° C./hr so that strain is applied to the sputtering target, whereby magnetic permeability can be reduced. Example 189 describes subjecting the Ni—P alloy powder prepared via gas atomization to HIP (hot isostatic pressing) at 950° C., but a liquid phase will be generated at this kind of high temperature, and the product cannot be processed into a target shape since the texture will be brittle.
Meanwhile, when a Ni—P alloy is melted and atomized as described above, a large amount of P will evaporate, and there is a problem in that an atomized powder having a composition that differs (deviated) from the intended composition will be formed. And when this kind of atomized powder having such a compositional deviation is subject to hot pressing or hot isostatic pressing, there is a problem in that the composition in the obtained target becomes uneven. Furthermore, there is a problem in that the density cannot be increased, and a high density target cannot be obtained.
Moreover, the present Applicant previously provided the following technology regarding a Ni alloy sputtering target. Patent Document 4 provides a technique of, by increasing the purity of the Ni—Pt alloy, considerably reducing the hardness of a Ni—Pt alloy ingot to enable rolling, and stably and efficiently producing a rolled target. Moreover, Patent Document 5 provides a nickel alloy target that does not contain any coarse crystal grains as a result of subjecting a nickel alloy ingot to forging, rolling and other processes.
These technologies exhibit a superior effect of being able to prevent the generation of fractures and cracks of a target and considerably suppress the generation of particles caused by the abnormal discharge during sputtering in comparison to targets produced based on conventional methods, but there were limitations inevitably to suppress the grain boundary fractures that are generated upon rolling the nickel alloy because a nickel alloy itself has the property of being extremely hard and brittle.